Invitation (Chōsen 挑戦) is the eighteenth episode of the Accel World Anime. It aired August 10th 2012 in Japan.
Over in Okinawa, Kuroyukihime is on her school trip with her friend Megumi. As the two go souvenir shopping for each other, Kuroyukihime is approached by two local Burst Linkers, Ruka Asato and Itosu Mana, who ask her to help their master fight against a monster that is plaguing their Accel community. The discussion causes Kuroyukihime to lose track of time and forget to buy Megumi a present, which upsets her. Kuroyukihime apologises to Megumi by telling her that, since discovering Brain Burst seven years ago, she is the one who kept her tied to the real world. The next day, Kuroyukihime enters the Accelerated World with Ruka and Itosu to meet up with their master, who turns out to be an old acquaintance of Kuroyukihime's, Crimson Kingbolt.